A fuel cell is provided with a fuel electrode, an oxidizing agent electrode, and an electrolyte membrane provided therebetween. Fuel is supplied to the fuel electrode, and an oxidizing agent is supplied to the oxidizing agent electrode, thereby electric power generated by electrochemical reaction. Although hydrogen is generally used as the fuel, a direct type fuel cell, which directly uses alcohol such as methanol and the like being inexpensive and being easily treated as the fuel, has been also actively developed in recent years.
When the hydrogen is used as the fuel, the reaction in the fuel electrode is represented by the following formula (1).3H2→6H++6e−  (1)
When the methanol is used as the fuel, the reaction in the fuel electrode is represented by the following formula (2).CH3OH+H2O→6H++CO2+6e−  (2)
Also, in any case, the reaction in the oxidizing agent electrode is represented by the following formula (3).3/202+6H++6e−→3H2O  (3)
In particularly, since hydrogen ions can be obtained from an alcoholic solution in the direct type fuel cell, a reformer and the like become unnecessary and the miniaturization and weight saving of the fuel cell can be attained. Also, the direct type fuel cell has an advantage that the energy density of the fuel cell is very high since the fuel cell uses the liquid alcoholic solution as the fuel.
Japanese Unexamined Patent Publication No. 2002-216823 discloses a fuel cell provided with means adapted to close the circulation of the air at the time of stopping the fuel cell in an air supply line for supplying air to an air electrode of the fuel cell and an air discharge line for discharging the air from the air electrode. According to the conventional examples, the dryness of an electrolyte during the operation stop of the fuel cell can be prevented.
However, when the oxidizing agent electrode is constituted to be opened in the direct type fuel cell using liquid fuel such as the methanol and the like as the fuel, the direct type fuel cell has a problem that the fuel passes through the electrolyte membrane during the stop of the fuel cell and is evaporated at the oxidizing agent electrode side.